This paper uses a new survey to contrast the wages of genetically
identical twins with different schooling levels. Multiple measurements of
schooling levels were also collected to assess the effect of reporting
error on the estimated economic returns to schooling. The data indicate
that omitted ability variables do not bias the estimated return to
schooling upward, but that measurement error does bias it downward.
Adjustment for measurement error indicates that an additional year of
schooling increases wages by 12-l6t, a higher estimate of the economic
returns to schooling than has been previously found.